The major goal of the effective vaccine development is to maximize the generation of protective antibody responses and to develop long-lasting humoral immunity. Germinal center (GC) reaction is the hallmark of humoral immunity involving tight interaction between B and T cells. Specifically, a specialized T cell subset, follicular helpr T (Tfh) cells, was shown to play pivotal roles in providing crucial help to GC B cells, thereby enabling them to differentiate into high affinity antibody-producing plasma cells and memory B cells. To date, GC B cells and Tfh cells were found to express many similar molecular features including cell surface molecules, transcription factors and microRNAs (miRNAs). Like transcription factors, recent studies investigating the role of miRNAs, a subset of small regulatory RNA species, have demonstrated that they can act as important molecular regulators in the immune system. Our preliminary studies have shown that mice devoid of miR-146a, a miRNA highly expressed in both GC B cells and Tfh cells, exhibited increased GC responses, suggesting a negative regulatory role of miR-146a in controlling GC reactions. Here, we propose a multifaceted study employing genetic, biochemical, immunological approaches and whole animal experimentation to comprehensively examine the role for miR-146a in T cell-dependent B cell-mediated humoral immunity. At the cellular level, by generating new mouse models with miR-146a ablation in different immune subsets, we will study the role of miR-146a in controlling GC responses in defined immune cell populations. At the molecular level, we will examine known miR-146a targets as well as identify new key molecules that contribute to miR-146a-regulated GC responses. Collectively, the proposed study will greatly improve our understanding of miRNA-mediated immune regulation during crucial phases of T cell-dependent humoral immunity. Ultimately, the long-term goal of our research is to develop successful strategies aimed at targeting miRNA-mediated gene regulatory machineries in the immune system to generate robust and long-lasting immune responses against a wide array of invading microorganisms.